1. The Field of the Invention
The invention generally relates to the field of temporarily implantable blood filters for prevention of pulmonary embolism.
2. Background and Relevant Art
Pulmonary embolism (PE) oftentimes can cause hospital deaths, which may be preventable. PE is responsible for an estimated 100,000 fatalities in USA every year. PE is typically caused by an embolization of the pulmonary artery, which can lead to right cardiac ventricular overload and acute heart failure. Frequently, the underlying cause is migration of a fragment of clot, originating from a vein in one of the legs, which reaches the pulmonary artery through the Vena Cava. In less frequent cases, other emboli like fragments of fatty tissue have been observed.
The pulmonary circulation is equipped to handle clot fragments of a certain size through thrombolysis, but generally fragments of more than 5 mm in diameter are considered a risk factor for PE. Frequently, patients may be at transient risk for PE, for instance, during the treatment of certain cancers or after orthopedic surgery. In such cases, a temporary implantation of a blood filter, such as a Vena Cava filter, has been shown to lead to a dramatic reduction in the incidents of PE. Typically, such blood filters are umbrella or cage-like structures, designed for temporary implantation, and with the ability to filter emboli greater than a certain cut-off size. Normally, the blood filter is percutaneously implanted and removed with delivery and retrieval catheters.
One of the challenges of typical Vena Cava filters is combining secure anchoring of the device in the implantation phase with reliable retrievability after the at-risk period has passed. In some instances, blood filters have hollow filter legs containing deployable anchor wires. Upon insertion of the catheter and positioning of the device, the filter is advanced out of the catheter to allow the hollow legs to expand and position themselves against the vessel wall. Next, the anchor wires are advanced out of the hollow legs. A preset curvature allows the anchor wires to assume an anchoring configuration, which enables the user to use the anchor wires to engage the vessel wall. Retrieval of the blood filter is achieved by performing the procedure in the reverse order. In this configuration, the thickness of the anchor wires is limited by the size of the hollow legs, and the location of the anchor wires is limited to the distal end of the hollow legs.
The Vena Cava is a notoriously mobile organ. Thus, preventing migration of the blood filter away from the site of implantation and preventing misalignment of the blood filter from tilt-and-shift events remains one of the challenges of Vena Cava filter design. Particularly, anchoring the blood filter with aggressive tissue anchors is limited by the need of reliable retrieval of the blood filter. As complications may occur during the retrieval of the blood filter, in many cases the risk of retrieval may be higher than the risk of leaving the blood filter in place. Accordingly, there are a number of disadvantages in blood filter design that can be addressed.